Method and Device For Attaching a Subsea Cutting Apparatus

ABSTRACT

A method of and a device for attaching a cutting apparatus, the cutting apparatus comprising a framework structure and a cutting head which can be displaced relative to the framework structure, and where, during the cutting operation, the cutting apparatus is tied in to the seabed by means of at least one attachment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and is a U.S. National Phase ofPCT International Application Number PCT/NO2005/000107, filed on Mar.29, 2005. The disclosure of the above-referenced application is herebyexpressly incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

This invention regards a method of attaching a subsea cutting apparatus.More particularly, it regards a method in which a cutting apparatusdesigned to cut an object is attached to the seabed. The invention alsocomprises a device for implementing the method.

Cutting of objects located under water can according to prior art beaccomplished by e.g. sawing, grinding, clipping or burning.

The cutting operation is normally performed by placing a cuttingapparatus at the cutting site by means of e.g. lifting equipment or aso-called ROV (Remote Operated Vehicle). Then the cutting apparatus mayoptionally be connected to the object to be cut. It has proven to berather difficult to achieve satisfactory attachment of a cuttingapparatus by remote control, when using prior art.

For reasons of safety, the actual cutting operation is normallycontrolled from a location remote from the cutting site, preferably fromthe surface of the sea.

It is also known to place a cutting apparatus on the seabed duringcutting operations. This may prove satisfactory when clipping an object,but as a rule it will not provide sufficient stability when cutting theobject by means of sawing or grinding.

SUMMARY OF THE INVENTION

The object of the invention is to remedy or reduce at least one of thedisadvantages of prior art.

The object is achieved in accordance with the invention, by thecharacteristics stated in the description below and in the followingclaims.

A framework structure is placed on or immediately above the seabed bythe object to be cut. The framework structure is provided with a cuttinghead arranged to be displaced (advanced) in the direction of the objectto be cut, in a manner that is known per se.

The cutting head may, in dependence of the cutting method employed,comprise e.g. cutting tools that represent prior art per se, such as adiamond wire saw, a saw blade saw, a grinding rig in which is used anabrasive wheel or a fluid to which has been added an abrasive.Alternatively the cutting head may comprise torch equipment based on gasor electricity. It may also be appropriate to combine various cuttingequipment.

The framework structure is provided with at least one fastener portionarranged to be coupled to an attachment projecting into the seabed.

Most preferably the attachment is brought to the seabed along with thecutting apparatus. When the cutting apparatus is in a planned positionthe attachment or attachments can be moved into the seabed. Whenattached to the seabed, the attachments are made to accommodate theforces transferred from the cutting head to the framework structure.

The attachment may be pre-mounted at the mounting site and may inaddition to the attachment also comprise a coupling portion for couplingto the framework structure.

Advantageously the attachment is designed as a suction anchor or aground screw. In special cases other solutions such as a pile or hooksmay be appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS

The following describes a non-limiting example of a preferred method andembodiment illustrated in the accompanying drawings, in which:

FIG. 1 is a plan view of a cutting apparatus placed in position about anobject to be cut;

FIG. 2 is a side view 1 a-1 a of FIG. 1;

FIG. 3 is a side view 1 b-1 b of FIG. 1;

FIG. 4 shows the same as FIG. 1, but here the object has been partiallycut;

FIG. 5 shows a cutting apparatus equipped with ground screws; and

FIG. 6 shows a cutting apparatus equipped with piles.

In the drawings, reference number 1 denotes a cutting apparatuscomprising a framework structure 2 and a cutting head 4 displaceablycoupled to the framework structure.

The framework structure 2 comprises two parallel spaced-apart framemembers 6. The frame members 6 are assembled by means of a cross member8 extending between the frame members 6 near one end of the framemembers 6. The cross member 8 and the frame members 6 together form anopen U-shape. Thus the framework structure 2 can be moved in across anobject 10 to be cut, so that the object 10 will be between the framemembers 6, see FIG. 1.

The frame members 6 each have a rail 12, which rails are mutuallyparallel. The rails 12 are a complementary fit to drive and runningwheels (not shown) provided in the wheelhouses 16 of the cutting head 4.

The wheelhouses 16 are rigidly interconnected by a profile 18. Thewheelhouses 16 also form the supports for the driving disk 20 andreversing disk 22, respectively, of the cutting head.

The driving disk 20 is connected to a driving motor 24. A sawing wire 26preferably provided with diamond cutting means runs endlessly around thedisks 20, 22.

The outside of the framework structure 2 has a number of fastenerportions 28, here three, for coupling to respective attachments 30.

In this preferred embodiment the attachments 30 are suction anchors 32.

The required control and power connections to the cutting apparatus 1are of a type that is known per se, and are not shown.

When an object 10 is to be cut the cutting apparatus 1 is placed on theseabed about the object 10. The suction anchors 30 are moved into theseabed 34 in a manner that is known per se, by removing the waterpresent inside the suction anchor 30. This results in a negativepressure in the suction anchor 30, causing the suction anchor 30 to moveinto the seabed 34.

After the cutting apparatus 1 has been tied in to the seabed the drivingmotor 24 is started, thus causing the sawing wire 26 to rotate about thedisks 20, 22. Then the cutting head 4 is advanced towards the object 10,whereby the sawing wire 26 cuts into the body of the object 10, see FIG.4.

When the cutting has been completed the sawed-off part of the object 10may be removed, whereupon the cutting apparatus 1 can be released fromthe seabed 34.

In an alternative embodiment, see FIG. 5, the cutting apparatus 1 isprovided with ground screws 36. The ground screws are designed with ascrew thread 38 and are arranged to be screwed into the seabed 34 byturning the ground screw 36 about its own longitudinal axis. The groundscrew 36 extends rotatably through a through opening 40 in the fastenerpart 28.

In another embodiment the cutting apparatus 1 is provided with piles 42extending through respective openings 40 and into the seabed 34, seeFIG. 6.

1. A method of attaching a cutting apparatus to the seabed, the cuttingapparatus comprising a framework structure for enclosing an object to becut and a cutting head which can be displaced relative to the frameworkstructure, the method comprising providing at least one attachment anddeploying the anchor(s) so that during the cutting operation, thecutting apparatus is tied in to the seabed during the cutting operationat least one attachment comprising at least one suction anchor.
 2. Adevice for attaching a cutting apparatus to the seabed, the cuttingapparatus comprising a framework structure for enclosing an object to becut and a cutting head which can be displaced relative to the frameworkstructure at least one attachment that can projects into the seabed thatthe attachment comprising at least one suction anchor so that during thecutting operation, the cutting apparatus is tied in to the seabed.
 3. Adevice in accordance with claim 2, wherein the cutting apparatus isprovided with a sawing wire comprising diamond cutting surfaces.
 4. Adevice in accordance with claim 2, wherein the cutting apparatus isprovided with a source of a cutting medium in the form of a fluid towhich has been added an abrasive.
 5. A method in accordance with claim1, wherein the framework structure comprising two generally parallel,spaced apart frame members and a cross member extending between them toform an open u-shape, the method further comprising the step ofenclosing the object to be cut by moving the framework structure so thatthe object enters the opening of the u-shape to be positioned betweenthe spaced apart frame members.
 6. A method in accordance to claim 5,wherein the spaced apart frame members each carry a rail and the cuttingapparatus comprises running wheel in engagement with the rails and acutting head mounted upon the wheels, the cutting head incorporating acutting mechanism, the method including the further step of causing thecutting head to travel along the rails by means of the running wheels tobring the cutting mechanism into contact with the object to be cut.
 7. Adevice in accordance with claim 2, wherein the framework structurecomprising two generally parallel, spaced apart frame members and across member extending between them to form an open u-shape, configuredso that the object can enter the opening of the u-shape to be positionedbetween the spaced apart frame members.
 8. A device in accordance toclaim 7, wherein the spaced apart frame members each carry a rail andthe cutting apparatus comprises running wheels in engagement with therails and a cutting head mounted upon the wheels, the cutting headincorporating a cutting mechanism, the cutting head being configured totravel along the rails by means of the running wheels to bring thecutting mechanism into contact with the object to be cut.